The Role of Parasympathetic Modulation of the Reentrant Arrhythmic Substrate in the Genesis of Sustained Ventricular Tachycardia

The influence of parasympathetic activity on the reentrant arrhythmic substrate in the genesis of sustained ventricular tachycardia remains unclear. To assess this influence, we studied the heart rate variability in 59 patients referred for invasive electrophysiological testing. In addition, the presence of late potentials and high grade ventricular ectopy, and the left ventricular ejection fraction was determined. The 28 patients with inducible sustained ventricular tachycardia were found to have lower heart rate variability by time- and frequency-domain measurements over 24 hours when compared to the 31 subjects who were noninducible. PNN50 was 4% in the inducible patients, whereas it was 9% in the subjects who were noninducible (P = 0.03). Similarly, HFP24H was 9 and 14 msec, respectively (P = 0.02). MAXHFP1H also differed (20 vs 27 msec [P = 0.04]) but not MINHFP1H (5 vs 6 msec). There was no association between heart rate variability and late potentials, degree of ventricular ectopy, or left ventricular ejection fraction. Thus, vagal tone does not appear to correlate with the presence of late potentials, ventricular ectopy, or left ventricular dysfunction. Low mean as well as maximal vagal tone, in contrast to minimal vagal tone, predicts inducibility of sustained ventricular tachycardia. Our data suggest that the inability to modulate parasympathetic tone appears to be an important determinant in the genesis of reentrant sustained ventricular tachycardia.     

Steroid-Tipped Leads Versus Porous Platinum Permanent Pacemaker Leads: A Controlled Study

WISH, M., ET AL.: Steroid-Tipped Leads Versus Porous Platinum Permanent Pacemaker Leads: A Controlled Study. There is little data directly comparing steroid-tipped permanent pacemaker leads to otherwise state-of-the-art porous platinum leads. Eighteen patients receiving unipolar generators capable of low voltage outputs were randomized at the time of implant to receive either steroid-tipped leads or porous platinum leads. All leads were unipolar, tined, passive fixation, and placed in the right ventricular apex or atrial appendage. This study is single center. At implant, threshold pulse width was determined at 3 voltages (2.5, 1.5, and 0.8 V). Follow-up thresholds were determined at weeks 1, 2, 3, and 4, and at 3 and 6 months. There was no difference in implant thresholds or amplitudes for sensing. By 2 weeks postimplant, lower thresholds were noted for the steroid leads, and this discrepancy grew more significant with time. There was no significant postimplant rise in threshold for steroid-tipped leads. At 6 months, the average threshold pulse width for ventricular steroid leads at 0.8 V was 0.3 ± 0.1 msec. In contrast, five patients with standard leads did not capture at maximum pulse width at 0.8 V (p < 0.0001). There was no significant difference in the amplitude of the chronic atrial electrogram. This study shows steroid-tipped leads to offer a significant advantage in reducing thresholds early postimplant and chronically.     

Broad Applicability of Ultrarapid Train Stimulation as an Efficient Alternative to Conventional Programmed Electrical Stimulation

FISHER, J.D., et al.: Broad Applicability of Ultrarapid Train Stimulation as an Efficient Alternative to Conventional Programmed Electrical Stimulation. Background and study objective:Conventional programmed electrical stimulation (PES) is useful for establishing inducibility or noninducibility of clinical ventricular arrhythmias (VA), but is complex and time-consuming. This study compared a standard PES protocol with ultrarapid train stimulation (UTS) in a broad range of patients with and without a history of ventricular arrhythmias or structural heart disease. Methods: Patients prospectively underwent electrophysiologic testing with both UTS and conventional PES protocols in a randomized, crossover design. Results: The results were concordant in 79% of 150 matched pairs of comparisons in 104 patients (NS). There were no differences related to underlying heart disease or arrhythmia, or antiarrhythmic treatment. Induction of nonclinical arrhythmias with the two methods was similar   (P = 0.524)   . Inhibition phenomena were minor except in some patients receiving amiodarone. Fewer drive-extrastimuli sequences and less time were needed to complete the trains protocol   (P < 0.0001)   . Conclusions: In cases where the main intent is to induce ventricular arrhythmias, UTS yields results that are similar to those of conventional PES protocols in a shorter length of time. (PACE 2003; 26[Pt. II]:518–523)     

Supraventricular Arrhythmias in Children and Young Adults with Implantable Cardioverter Defibrillators

INTRODUCTION: Rapidly conducted supraventricular tachycardias (SVTs) can lead to inappropriate device therapy in implantable cardioverter defibrillator (ICD) patients. We sought to determine the incidence of SVTs and the occurrence of inappropriate ICD therapy due to SVT in a pediatric and young adult population. METHODS AND RESULTS: We undertook a retrospective review of clinical course, Holter monitoring, and ICD interrogations of patients receiving ICD follow-up at our institution between March 1992 and December 1999. Of 81 new ICD implantations, 54 eligible patients (median age 16.5 years, range 1 to 48) were identified. Implantation indications included syncope and/or spontaneous/inducible ventricular arrhythmia with congenital heart disease (30), long QT syndrome (9), structurally normal heart (ventricular tachycardia/ventricular fibrillation [VT/VF]) (7), and cardiomyopathies (7). Sixteen patients (30%) received a dual-chamber ICD. SVT was recognized in 16 patients, with 12 of 16 having inducible or spontaneous atrial tachycardias. Eighteen patients (33%) received > or =1 appropriate shock(s) for VT/VF; 8 patients (15%) received inappropriate therapy for SVT. Therapies were altered after an inappropriate shock by increasing the detection time or rate and/or increasing beta-blocker dosage. No single-chamber ICD was initially programmed with detection enhancements, such as sudden onset, rate stability, or QRS discriminators. Only one dual-chamber defibrillator was programmed with an atrial discrimination algorithm. Appropriate ICD therapy was not withheld due to detection parameters or SVT discrimination programming. CONCLUSION: SVT in children and young adults with ICDs is common. Inappropriate shocks due to SVT can be curtailed even without dual-chamber devices or specific SVT discrimination algorithms.     

Characteristics of Sinus Rhythm Electrograms at Sites of Ablation of Ventricular Tachycardia Relative to All Other Sites: A Noncontact Mapping Study of the Entire Left Ventricle

Noncontact Mappin g of VT During Sinus Rhythm. Introduction : Regions of the diseased ventricle that activate abnormally during sinus rhythm (SR) may be the areas of slow and disorganized conduction that form the diastolic pathway through which reentry may occur during ventricular tachycardia (VT).
Methods and Results : We examined features of electrograms recorded during SR that might indicate a site suitable for ablation of VT using a noncontact mapping system, which enables reconstruction of > 3,000 electrograms. Preablation SR electrogram characteristics at sites of successful radiofrequency ablation (RFA) were examined in 13 patients with 53 VTs. Timing of onset, lateness of activity, electrogram duration, and number of baseline crossing events of reconstructed electrograms at the sites of successful RFA were compared with the electrograms of latest onset, latest activity, longest duration, and most baseline crossing events of all ventricular sites. Onset of activation at sites of successful RFA were 26.9 ± 25.2 msec (mean ± SD) earlier than (and 2.9 ± 1.7 cm away from) the site of latest onset of SR activation. Electrogram duration at sites of successful RFA was 83%± 14.6% of (and 4.3 ± 1.8 cm away from) the longest electrogram. The baseline crossing events at sites of successful RFA were 53%± 22% of (and 4.9 ± 1.9 cm away from) the most fractionated electrogram. The latest activity at sites of successful RFA was 21.6 ± 24.8 msec earlier than (and 4.3 ± 1.6 cm away from) the site of latest activity.
Conclusion : Although the site of latest onset of endocardial activation during SR proved to be the most sensitive indicator, the characteristics of SR electrograms did not usefully predict successful ablation sites.     

Statistical Distribution of Ventricular Ectopic Beats Assessed by Computer Analysis of Long-Term Electrocardiograms: Problems Related to the Definition of Arrhythmogenesis

The severity and clinical importance of arrhythmogenic effects of antiarrhythmic drugs have been well recognized, but only empirical and naive approaches have been used to define antiarrhythmic and proarrhythmic effects when comparing baseline and on-therapy Holter recordings. This article suggests a new method for the assessment of these effects, based upon comparisons of statistical distributions of ectopic beats recorded on long-term electrocardiograms. Since these distributions are very individual, the Smirov test was used for their comparison. This enables the antiarrhythmic and arrhythmogenic effects to be defined on a precise statistical basis. To demonstrate this method, an analysis is reported of Holter recordings made on six patients suffering from different types of ventricular arrhythmia. In each of these patients, one baseline Holter recording and one recording on each of three different drugs (flecainide, sotalol, and verapamil) were made. The records were digitized using a commercially available system for the analysis of long-term electrocardiograms and random sampling was used to obtain independent samples of arrhythmic episodes that were subsequently statistically analyzed. The results show that the problem of the definition of arrhythmogenesis can be partly addressed in a precise mathematical way and that treatment with an antiarrhythmic preparation may not only have general antiarrhythmic or arrhythmogenic effects, but may also cause a significant change in the character of arrhythmia that can neither be classified as antiarrhythmic nor as arrhythmogenic influence. The clinical implications of this approach are discussed.     

Pernicious Anemia Caused by Crohn''s Disease of the Stomach

A patient with granulomatous gastritis is described. Two years after the presentation of his gastric disease he developed pernicious anemia. Lack of intrinsic factor production secondary to Crohn's disease of the stomach is felt to be the cause of his Vitamin B12 malabsorption.     

The Influence of Advertising on Tobacco Consumption: some problems with Chetwynd et al.'s analysis

In a recent study of the relationship between cigarette advertising and the aggregate consumption of cigarettes in New Zealand between 1973 and 1985, Chetwynd et al. (1988) argue that quarterly data suggest that advertising affects overall consumption of cigarettes with an elasticity of +0.07. In addition, they argue that advertising has a ‘carry over’ effect of about four quarters on current consumption. These results are potentially important for two reasons. Although the evidence is mixed, the conventional view is that cigarette advertising affects brand choice among smokers but not aggregate demand for cigarettes. Chetwynd et al.'s results, (hereafter, Chetmynd) contradict this traditional view. Secondly, if advertising does increase the aggregate demand for cigarettes, then a public policy banning cigarette advertising might reduce aggregate demand for cigarettes. Unfortunately, the Chetwynd, study is sufficiently flawed with conceptual and econometric problems that their inference that advertising increases cigarette demand is questionable. Certainly cigarette advertising may increase or decrease cigarette consumption. The point we wish to make is that, any inference one way or the other based on the results of Chetwynd, cannot be viewed as well-grounded in either scientific methodology or statistical principles.